The Earth Observatory image of the day for June 5 shows flooding in Botswana’s Savuti River and Savuti Swamp. The abundant water turns out to be a very small part of a much bigger picture.
The Savuti Swamp sits within the Kalahari Desert, which stretches across Namibia, Angola, Zambia, South Africa, and most of Botswana. More of a sandy savannah than an actual desert, the Kalahari has wet and dry seasons that cause significant differences in vegetation. When the region is plunged into drought, an inland river delta, the Okavango, provides life-sustaining water for the wildlife. Since 2009, that water supply has been more abundant than usual, and the water has overflowed into other waterways in the region.
In 2009, the Okavango started experiencing record floods. “We first saw good flooding in Lake Ngami a few years back,” said Frank Eckardt of the University of Cape Town. “We have seen the Boteti River in flood since 2009 and also water in Lake Xau, southeast of the Okavango Delta.”
The satellite images below were acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on April 28, 2012. The first image uses a combination of visible and infrared light to better distinguish between water and land. Water is navy blue, vegetation is bright green, and bare ground is earth-toned. The imagery shows not only abundant but early water: flows have arrived in the Okavango Detla well ahead of schedule (usually July) and the delta is overflowing.
The area outlined in white above is shown in this next close-up view of the Savuti channel and swamp that was featured as our image of the day. Impressive when well-watered, the swamp is in fact just a small part of a large network of rivers and basins.
“We had in concurrence the highest flood on record in the Cuando River and the flood in the Okavango River pushing through the Selinda Channel, the first time I have seen that documented,” said Guido van Langenhove of Hydrological Services Namibia. “The combined waters then reactivated the Linyanti River, which had been drying out since 1982, to reach the overflows/backwater of the Zambezi River through the Chobe River (Lake Liambezi).” Wetter conditions were apparent in the Bukalo Channel in 2011.
Van Langenhove explains that water has also started flowing through the Savuti Channel to the Mababe Depression, a 50-by-90-kilometer (30-by-60-mile) heart-shaped basin that normally receives little water.
The skinny strip of land jutting out from Namibia eastward is known as the Caprivi Strip. The Zambezi floodplain sits at the easternmost extent of this strip, and flooding occurred in that region before 2009.
Burrough, S.L., Thomas, D.S.G. (2008) Late Quaternary lake-level fluctuations in the Mababe Depression: Middle Kalahari palaeolakes and the role of Zambezi inflows. Quaternary Research, 69(3), 388-403.
Okavango-Delta.net. Okavango Delta Information. Accessed June 4, 2012.